In a system involving an electrically short vertical radiator, all elements of the antenna and an earthed ground are (for all practical purposes) electrically in series with each other. You can't resonate the ground system separately from the antenna itself.(Nor can you truly resonate the earth, in reality, to reduce losses. Last person who sincerely tried was Nikola Tesla, and he ended up impoverished, paranoid, and unloved, except allegedly by a pigeon.)
The entire goal of a LowFER ground system is to provide as low a resistance as possible to RF current returning to the transmitter that was sent out to the aerial. A large, low-loss inductor in the form of a variometer or a tunable LC circuit to resonate with the antenna's capacitance to ground is your best solution.
Nearly all the antenna current of a very short radiator is returned from within a radius not much larger than the height of the antenna. That means you don't need a lot of long radials, but do as many of them as you can of moderate length if you want to be heard at all.